Many steroid esters which have found applications in medicine are already known. The ester derivative is usually chosen for its effect of intensifying or prolonging the activity of the steroid used. A depot-effect is obtained on parenteral (subcutaneous or intramuscular) administration of steroid esters in solution; in this instance a slow absorption of the ester from the depot into the plasma takes place. In the plasma, or elsewhere in the body, the ester is hydrolysed and the steroid alcohol released may then, optionally after being metabolized, exert its action on the target organ.
The choice of the ester influences both the rate of absorption from the depot and the rate of hydrolysis in the body. The choice of the ester may also affect the administration form. For example, it is known from copending application Ser. No. 550,397 corresponding to Belgian Pat. No. 826,086 filed Feb. 2, 1975 that testosterone esters derived from aliphatic carboxylic acids with 9 to 16 carbon atoms are much more active than testosterone esters having less than 9 or more than 16 carbon atoms in the carboxylic acid residue when administered orally in the presence of a lipoid substance, for example a vegetable or an animal oil.